1. Field of the Invention
The present invention relates to a vehicle bumper system and method of making the same.
2. Description of the Related Art
Vehicle bumpers systems are generally designed to serve two functions. The first function is to protect the vehicle from damage due to low speed contacts with obstacles. Low speed collisions are generally defined as 5 miles per hour or less. The bumper system should withstand these low speed collisions without damage, either to the vehicle bumper system or to the vehicle. A secondary function of a vehicle bumper system is to manage energy in a higher speed collision to avoid or reduce injury to the vehicle passengers. High speed collisions are those greater than 5 miles per hour. High speed collisions will likely result in damage to either the vehicle bumper system or the vehicle. The way in which energy from the collision is managed through the bumper system and vehicle is designed to provide a repeatable and known collapse of the vehicle structure.
It is desirable to manufacture a bumper that is both lightweight and strong. Current lightweight bumpers are manufactured with injection molded plastic material. It is desirable to manufacture bumpers from a blow molded plastic material to further reduce the bumper weight and to use lower cost blow molding plastic materials. Several US patents have published designs for blow molded automotive bumper systems. U.S. Pat. No. 5,271,650 teaches a method of molding a blow molded bumper system having an integral attaching frame. The attaching frame is generally made of metal and serves to attach the bumper system to the vehicle. Two frames secure the bumper system to the vehicle. Each frame is mounted to the outer edge of the bumper system and serve to transmit collision energy through the bumper system to the vehicle.
It is useful to provide a vehicle bumper system that is both rigid across the frontal width of the vehicle for optimal energy management in a high speed collision, yet compliant to reduce damage in low speed collisions. Bumper systems as exemplified by U.S. Pat. Nos. 5,271,650 and 4,586,738, teaching unreinforced blow molded bumper systems attached the frontal edge of a vehicle. Making unreinforced bumpers sufficiently rigid to withstand both low speed collisions without damage and higher speed collisions with proper energy management requires the use of thick blow molded wall sections and thereby increasing material cost and bumper systems weight.
It has also been known to add foam within a vehicle bumper, as exemplified by U.S. Pat. No. 4,563,028. Foam stiffeners have been pre-molded and then assembled in place within the bumper. Use of pre-formed foam blocks require adhesives or fasteners and large access holes to attach the foam to the bumper system. It is desirable to place foam within a hollow bumper system without the need for adhesives, fasteners or large access holes.
It is further desirable to provide a vehicle bumper system that is capable of withstanding low speed collisions without damage, while providing a rigid cross-frontal area to controllably transmit energy from high speed collisions to the vehicle.